1. Field of the Invention
This invention relates to a device for draining static charges from the body of individuals prior to touching electronic equipment, and especially a device of such type which is useful for protecting the keypad of an electronic gasoline pump or an automatic teller machine.
2. Description of the Realated Art
Electronic gasoline dispensers became very popular in recent years. These dispensers are usually controlled by microprocessor boards which perform all functions from reading the credit card of the buyer to metering the flow of fuel. Automatic teller machines are also controlled by sophisticated microprocessor boards which can communicate with computers over a network, beside performing other functions such as delivering cash.
While such advanced technology for dispensing fuel or accessing a bank account offer flexibility and convenience to the public, thousands of unexplained failures of the microprocessor modules inside fuel dispensers and automatic teller machines are reported each year.
In the electronics industry, it is widely known that sensitive MOS devices can be damaged by voltages as little as 250 volts on the human body, if a charged body comes in contact with such devices. It has also been recognized for many years that an individual may become charged to voltages of up to 30,000 volts by simply moving across a car seat covered with velvet or a similar synthetic material. This is especially true in winter time, when the humidity is low. It has been established that electrostatic discharges generated by such elevated potentials on the human body not only can damage electronic devices directly, but can even pierce through thin layers of plastic, such as the plastic forming the keys of an electronic keyboard, and eventually reach the conductors leading to the sensitive components.
Unfortunately, little attention has been paid to the problem of frequent damage to sensitive computer modules inside gasoline dispensers and automatic teller machines by individuals who become charged electrostatically as they step out of their automobiles in dry weather.
In the prior art, several methods have been shown for the protection of electronic equipment from individuals who become charged to high voltages. U.S. Pat. No. 4,303,960 issued Dec. 1, 1981 to Sherwood et al. shows a method for protecting a keypad from electrostatic discharges which is based on providing a conductive sheet over the face of the keypad for draining static charges from the body of the user. Practically, however, such method proved to be not completely successful, since electrostatic discharges generated by high voltage can find multiple discharge paths to ground, one of which could possibly be through the circuit which is intended to be protected. Further, strong electrostatic discharges can disrupt or even wipe completely a program stored in a computer module by electromagnetic coupling. Moreover, it has been shown that static charges on the human body can often damage sensitive MOS devices simply by induction.
U.S. Pat. No. 4,586,106 issued Apr. 29, 1986 to Thomas G. Frazier shows a static dissipative touch device that consists essentially of a conductive strip which is to be attached or glued to the electronic equipment which is to be protected. The conductive strip carries a message to attract the attention of the user, such as "Touch me first", and must be touched by the user prior to touching the equipment. Clearly, such method will not protect equipment intended for public use, such as gasoline pumps or automatic teller machines, since the user will simply ignore such device and proceed directly to touching the equipment.
It is the objective of the present invention to provide an effective and reliable method and mechanism for draining static charges from the bodies of individuals prior to touching equipment placed in public locations. It is another objective of the present invention to provide a mechanism which will protect electronic equipment completely from the other effects associated with static, such as induction or electromagnetic coupling.
Other objectives and features of the invention will become fully apparent from the ensuing disclosure and appended claims.